Sherlock Holmes stories

The series is filled with proofs with the possibility of a romantic relationship between Sherlock and John. Notably, there is a dinner conversation where John thinks Sherlock is into men and Sherlock thinks John is coming on to him, so Sherlock gently (!) explains that he is "married to [his] work." A number of other characters assume that the two are a couple, such as the restaurant manager thinking the two are on a date, and Mrs. Hudson thinking that they might share a bedroom.

In the second episode, there is some tension surrounding John going on a date with Sarah, one which Sherlock ends up inviting himself along for.

In the third episode, it is established by Moriarty that John is Sherlock's "heart".

In series two, there are several examples of Sherlock and John's implied status as a couple. Episode one has John deny their status as a couple but Irene Adler insists that they are. As well, when John is speaking with his girlfriend, she tells him "You really are a good boyfriend... Sherlock Holmes is a lucky man," implying that he is devoted to Sherlock instead. There is a lot of speculation on Sherlock's sexuality in this episode as well. We are also given a scene with Mycroft snidely saying "how would you know?" to Sherlock's reply of "sex doesn't alarm me," to be later paired with Jim's nickname of "The Virgin."

Episode two has the inkeepers mistake John and Sherlock for a gay couple, apologizing for not getting them a double room.

Episode three has newspaper articles that say Sherlock has been seen frequently in the company of "confirmed bachelor John Watson" (an old fashioned term for closeted gay man).

Fanon

While the Sherlock Holmes fandom is one of the oldest, most venerable fandoms, and mainstream besides, Johnlock is the most popular pairing in the fandom. Fannish interest in the pairing has increased recently following the Sherlock Holmes 2009 film and the BBC's 2010 TV series Sherlock.

A variety of portrayals of Sherlock and John's sexualities and their relationship are common in fandom. One very common plot of fanwork is the usually romantic storyline of how Sherlock and John come to discover their romantic and sexual attraction to one another. Some of these stories are framed with Sherlock doing an "experiment" of some sort. The experiment is sometimes either sexual or has a physical element that requires close contact, and John is required to participate or is sometimes annoyed or blackmailed into participating. These frequently lead to a consensual intimate or sexual experience in which they confess their feelings. Romantic fan fiction about Sherlock's anticipated return after Reichenbach also often follow the pattern of Sherlock and John slowing revealing their unacted-upon romantic feelings for one another.

Other fanworks explore Sherlock and John's very close but platonic relationship. Such fics might be labelled 'friendship fic,' 'Pre-slash' or 'bromance' in order to indicate the relationship being explored is neither traditionally romantic or sexual. Common tropes include John and Sherlock platonically sharing the same bed, cuddling, and getting married out of convenience.